Update instances of "Mining" with "Earning"

[Siegfried-B]

We need to replace "Mining" with "Earning" - post migration, we don't mine any more.

[jthiller]

I was on the fence about this change, but the social consensus seems to be that "earn" is the preferred term. Let's use this PR to encapsulate this change across the repository.

[Dumpling-girl]

If I see it passing by in texts I will edit it.